The present invention relates to monitoring equipment for processing of liquids intended for human consumption, e.g., dairy products such as milk, cream, and ice cream mix, other liquid food products, e.g., fruit juices and soups, or pharmaceuticals. The invention is more particularly concerned with an adapter and a technique for employing a conventional diaphragm-type pressure gauge on sanitary conduits in which such liquid products are processed. The invention concerns an adapter that isolates the diaphragm of the pressure gauge out of direct contact with the process fluid (and out of contact with any caustic cleaning fluids) and which permits a given size of pressure gauge to be fitted onto conduits of a variety of diameters. The present invention also provides a positive visual indication of a failure of a pressure diaphragm or of a seal within the adapter.
Pasteurization is a process for heat treating milk or other food or ingestible product in order to kill pathogens such as bacteria or other microorganisms. The U.S. Public Health Service has published standards for equipment for the pasteurization of milk and other milk products, and there are similar regulations concerning equipment for processing other products. By law, the milk or other product has to be heated to certain temperatures and held at a particular temperature. The pressures and pressure differentials of the product have to be closely monitored at certain points in the process. This means that working pressure gauges have to be present in the conduit, and must be replaced whenever they fail. On the other hand, in order to ensure that the sanitary conduit can be cleansed and sanitized between processes, the conduit is designed so that it can be completely cleaned of any milk or other product by washing it and rinsing it with a cleaning fluid that must reach every point on the interior of the conduit. The cleaning process usually involves a highly caustic component to remove food particles from the walls of the conduit. No threaded connectors can be used anywhere that the liquid product flows, because of the difficulty in cleaning the threads. Standard pressure gauges typically have a threaded stem that is used for securing the gauge into a threaded nipple in the associated equipment. Because there can not legally be any threaded connections at any point at which the product would come into contact with the threads, the standard practice is to use a diaphragm type pressure gauge, instead. This type gauge has a circular fitting foot with a diaphragm and flange disk, and this circular foot is attached, using a tri-clamp or sanitary clamp, on top of an annular flange portion of a stub member that is affixed onto the conduit. The sanitary clamp, or so-called tri-clamp, compresses a sealing gland or ring between these two flanges, so there are no threads exposed to the product in the sanitary conduit. These specially constructed gauges are many times more costly than the standard pressure gauges, and are expensive to replace. In addition, most food processing plants have to keep a variety of pressure gauges in supply, with a variety of diameters of their fitting foot portion, in order to accommodate a variety of diameters of sanitary conduit.
In addition, the diaphragm type gauges mentioned above do not have any means for disclosing a leak or a failure of a seal within the gauge assembly. The liquid food product and the caustic cleaning solution can each cause corrosion of the material used in the pressure transmitting diaphragm. Usually this is a stainless steel, but even so diaphragms fail on may of these pressure gauges in use at dairies, pharmaceutical plants, and elsewhere. Failure of the diaphragm can cause liquid within the gauge to leak out, which can contaminate the food product.
In a regenerative heat exchanger of the type that is used in many pasteurizers, critical temperature differences have to be maintained. To achieve this, flow rates must be kept within narrow limits, which requires critical pressure differentials. For efficient operation it is important to monitor pressure there very closely. It is also desirable to be able to replace a gauge quickly when it fails, and to employ only a single standard size of gauge, in combination with adapters to allow that gauge to be used at any of a number of points on the sanitary conduit.